Local Gamma-ray Bursts Research Articles

Identification of a Local Sample of Gamma-Ray Bursts Consistent with a Magnetar Giant Flare Origin

Abstract Cosmological gamma-ray bursts (GRBs) are known to arise from distinct progenitor channels: short GRBs mostly from neutron star mergers and long GRBs from a rare type of core-collapse supernova (CCSN) called collapsars. Highly magnetized neutron stars called magnetars also generate energetic, short-duration gamma-ray transients called magnetar giant flares (MGFs). Three have been observed from the Milky Way and its satellite galaxies, and they have long been suspected to constitute a third class of extragalactic GRBs. We report the unambiguous identification of a distinct population of four local (<5 Mpc) short GRBs, adding GRB 070222 to previously discussed events. While identified solely based on alignment with nearby star-forming galaxies, their rise time and isotropic energy release are independently inconsistent with the larger short GRB population at >99.9% confidence. These properties, the host galaxies, and nondetection in gravitational waves all point to an extragalactic MGF origin. Despite the small sample, the inferred volumetric rates for events above 4 × 1044 erg of Gpc−3 yr−1 make MGFs the dominant gamma-ray transient detected from extragalactic sources. As previously suggested, these rates imply that some magnetars produce multiple MGFs, providing a source of repeating GRBs. The rates and host galaxies favor common CCSN as key progenitors of magnetars.

Magnetar as Central Engine of Gamma-Ray Bursts: Quasi-universal Jet, Event Rate, and X-Ray Luminosity Function of Dipole Radiations

Abstract Early shallow-decaying X-ray afterglows of gamma-ray bursts (GRBs) may be attributed to the dipole radiations of newly born magnetars. Assuming that the GRB jets powered by magnetars are quasi-universal, we find that the jet structure can be parameterized as a uniform jet with a luminosity of (1σ) and an opening angle (50% confidence level), surrounding by a power-law decay component with an index of (1σ). The inferred local GRB rate is ρ = 9.6 Gpc−3 yr−1 by including both the typical GRBs and LL-GRBs as the same population. The typical viewing angle is 3.3°, and may be 20° ∼ 30° for LL-GRBs. The X-ray luminosity function of the dipole radiation wind can be empirically described by a broken power-law function with indices and broken at . In the case where the wind outflow is collimated and coaxial with the GRB jet, we find that the wind structure is similar to the GRB jet, i.e., , , and . The observed correlation between the prompt gamma-ray luminosity and X-ray luminosity of the wind may result from the viewing angle effect in such a jet–wind system. A discussion on surveys using the X-ray instruments on board the Einstein Probe mission in the soft X-ray band for the jet and wind emission is also presented.

The luminosity function and formation rate of a complete sample of long gamma-ray bursts

ABSTRACT We study the luminosity function and formation rate of long gamma-ray bursts (GRBs) by using a maximum likelihood method. This is the first time this method is applied to a well-defined sample of GRBs that is complete in redshift. The sample is composed of 99 bursts detected by the Swift satellite, 81 of them with measured redshift and luminosity for a completeness level of $82\, {\rm per\, cent}$. We confirm that a strong redshift evolution in luminosity (with an evolution index of $\delta =2.22^{+0.32}_{-0.31}$) or in density ($\delta =1.92^{+0.20}_{-0.21}$) is needed in order to reproduce the observations well. But since the predicted redshift and luminosity distributions in the two scenarios are very similar, it is difficult to distinguish between these two kinds of evolutions only on the basis of the current sample. Furthermore, we also consider an empirical density case in which the GRB rate density is directly described as a broken power-law function and the luminosity function is taken to be non-evolving. In this case, we find that the GRB formation rate rises like $(1+z)^{3.85^{+0.48}_{-0.45}}$ for $z\lesssim 2$ and is proportional to $(1+z)^{-1.07^{+0.98}_{-1.12}}$ for $z\gtrsim 2$. The local GRB rate is $1.49^{+0.63}_{-0.64}$ Gpc−3 yr−1. The GRB rate may be consistent with the cosmic star formation rate (SFR) at $z\lesssim 2$, but shows an enhancement compared to the SFR at $z\gtrsim 2$.

Spectral properties of gamma-ray bursts observed by the Suzaku wide-band all-sky monitor

Abstract We have systematically studied the spectral properties of 302 localized gamma-ray bursts (GRBs) observed by the Suzaku wide-band all-sky monitor (WAM) from 2005 August to 2010 December. The energy spectra in the 100–5000 keV range integrated over the entire emission and the 1 s peak were fitted by three models: a single power law, a power law with an exponential cutoff (CPL), and the GRB Band function (GRB). Most of the burst spectra were well fitted by a single power law. The average photon index α was −2.11 and −1.73 for long and short bursts, respectively. For the CPL and GRB models, the low-energy and high-energy photon indices (α and β) for the entire emission spectra were consistent with previous measurements. The averages of the α and β were −0.90 and −2.65 for long-duration GRBs, while the average α was −0.55 and the β was not well constrained for short-duration GRBs. However, the average peak energy Epeak was 645 and 1286 keV for long- and short-duration GRBs respectively, which are higher than previous Fermi/GBM measurements (285 keV and 736 keV). The α and Epeak of the 1 s peak spectra were larger, i.e., the spectra were harder, than the total fluence spectra. Spectral simulations based on Fermi-GBM results suggest that the higher Epeaks measured by the Suzaku WAM could be due to detector selection bias, mainly caused by the limited energy range above 100 keV.

2900 Square Degree Search for the Optical Counterpart of Short Gamma-Ray Burst GRB 180523B with the Zwicky Transient Facility

There is significant interest in the models for production of short gamma-ray bursts (GRBs). Until now, the number of known short GRBs with multi-wavelength afterglows has been small. While the Fermi GRB Monitor detects many GRBs relative to the Neil Gehrels Swift Observatory, the large localization regions makes the search for counterparts difficult. With the Zwicky Transient Facility (ZTF) recently achieving first light, it is now fruitful to use its combination of depth (mAB ∼ 20.6), field of view (≈47 square degrees), and survey cadence (every ∼3 days) to perform Target of Opportunity observations. We demonstrate this capability on GRB 180523B, which was recently announced by the Fermi GRB Monitor as a short GRB. ZTF imaged ≈2900 square degrees of the localization region, resulting in the coverage of 61.6% of the enclosed probability over two nights to a depth of mAB ∼ 20.5. We characterized 14 previously unidentified transients, and none were found to be consistent with a short GRB counterpart. This search with the ZTF shows it is an efficient camera for searching for coarsely localized short GRB and gravitational-wave counterparts, allowing for a sensitive search with minimal interruption to its nominal cadence.

The second-closest gamma-ray burst: sub-luminous GRB 111005A with no supernova in a super-solar metallicity environment

We report the detection of the radio afterglow of a long gamma-ray burst (GRB) 111005A at 5-345 GHz, including very long baseline interferometry observations with a positional error of 0.2 mas. The afterglow position is coincident with the disc of a galaxy ESO 58049 at z = 0.01326 (∼1″ from its centre), which makes GRB 111005A the second-closest GRB known to date, after GRB 980425. The radio afterglow of GRB 111005A was an order of magnitude less luminous than those of local low-luminosity GRBs, and obviously less luminous than those of cosmological GRBs. The radio flux was approximately constant and then experienced an unusually rapid decay a month after the GRB explosion. Similarly to only two other GRBs, we did not find the associated supernovae (SNe), despite deep near- and mid-infrared observations 1-9 days after the GRB explosion, reaching ∼20 times fainter than other SNe associated with GRBs. Moreover, we measured a twice-solar metallicity for the GRB location. The low y-ray and radio luminosities, rapid decay, lack of a SN, and super-solar metallicity suggest that GRB 111005A represents a rare class of GRB that is different from typical core-collapse events. We modelled the spectral energy distribution of the GRB 111005A host finding that it is a moderately star-forming dwarf galaxy, similar to the host of GRB 980425. The existence of two local GRBs in such galaxies is still consistent with the hypothesis that the GRB rate is proportional to the cosmic star formation rate (SFR) density, but suggests that the GRB rate is biased towards low SFRs. Using the far-infrared detection of ESO 580-49, we conclude that the hosts of both GRBs 111005A and 980425 exhibit lower dust content than what would be expected from their stellar masses and optical colors.

GRB 170817A: a short GRB seen off-axis

The angular distribution of gamma-ray burst (GRB) jets is not yet clear. The observed luminosity of GRB 170817A is the lowest among all known short GRBs, which is best explained by the fact that our line of sight is outside of the jet opening angle, θobs > θj, where θobs is the angle between our line of sight and the jet axis. As inferred by gravitational wave observations, as well as radio and X-ray afterglow modeling of GRB 170817A, it is likely that θobs ∼ 20° – 28°. In this work, we quantitatively consider two scenarios of angular energy distribution of GRB ejecta: a top-hat jet and a structured jet with a power law index s. For the top-hat jet model, we get a large θj (e.g., θj > 10°), a rather high local (i.e., z < 0.01) short GRB rate ∼8–15×103, Gpc−3, yr−1 (estimated to be 90∼1850 Gpc−3, yr−1 in Fong et al.) and an extremely high Epeak,0 (on-axis, rest-frame) > 7.5 × 104, keV (∼500, keV for a typical short GRB). For the structured jet model, we use θobs to give limits on s and θj for typical on-axis luminosity of a short GRB (e.g., 1049 erg s−1 ∼ 1051 erg s−1), and a low on-axis luminosity case (e.g., 1049 erg s−1) gives more reasonable values of s. The structured jet model is more feasible for GRB 170817A than the top-hat jet model due to the rather high local short GRB rate, and the extremely high on-axis Epeak,0 almost rules out the top-hat jet model. GRB 170817A is likely a low on-axis luminosity GRB (1049 erg s−1) with a structured jet.

INVESTIGATION OF PRIMORDIAL BLACK HOLE BURSTS USING INTERPLANETARY NETWORK GAMMA-RAY BURSTS

ABSTRACT The detection of a gamma-ray burst (GRB) in the solar neighborhood would have very important implications for GRB phenomenology. The leading theories for cosmological GRBs would not be able to explain such events. The final bursts of evaporating primordial black holes (PBHs), however, would be a natural explanation for local GRBs. We present a novel technique that can constrain the distance to GRBs using detections from widely separated, non-imaging spacecraft. This method can determine the actual distance to the burst if it is local. We applied this method to constrain distances to a sample of 36 short-duration GRBs detected by the Interplanetary Network (IPN) that show observational properties that are expected from PBH evaporations. These bursts have minimum possible distances in the 1013–1018 cm (7–105 au) range, which are consistent with the expected PBH energetics and with a possible origin in the solar neighborhood, although none of the bursts can be unambiguously demonstrated to be local. Assuming that these bursts are real PBH events, we estimate lower limits on the PBH burst evaporation rate in the solar neighborhood.

MODELING THE SWIFT BAT TRIGGER ALGORITHM WITH MACHINE LEARNING*

ABSTRACT To draw inferences about gamma-ray burst (GRB) source populations based on Swift observations, it is essential to understand the detection efficiency of the Swift burst alert telescope (BAT). This study considers the problem of modeling the Swift/BAT triggering algorithm for long GRBs, a computationally expensive procedure, and models it using machine learning algorithms. A large sample of simulated GRBs from Lien et al. is used to train various models: random forests, boosted decision trees (with AdaBoost), support vector machines, and artificial neural networks. The best models have accuracies of ≳97% (≲3% error), which is a significant improvement on a cut in GRB flux, which has an accuracy of 89.6% (10.4% error). These models are then used to measure the detection efficiency of Swift as a function of redshift z, which is used to perform Bayesian parameter estimation on the GRB rate distribution. We find a local GRB rate density of n 0 &sim; 0.48 &minus; 0.23 &plus; 0.41 Gpc &minus; 3 yr &minus; 1 ?> with power-law indices of n 1 &sim; 1.7 &minus; 0.5 &plus; 0.6 ?> and n 2 &sim; &minus; 5.9 &minus; 0.1 &plus; 5.7 ?> for GRBs above and below a break point of z 1 &sim; 6.8 &minus; 3.2 &plus; 2.8 ?> . This methodology is able to improve upon earlier studies by more accurately modeling Swift detection and using this for fully Bayesian model fitting.

The search for high energy muon neutrinos from southern hemisphere gamma-ray bursts with BUST

The search for muon neutrinos with energy ≥1 GeV correlated with Gamma-Ray Bursts (GRBs) has been carried out at the Baksan Underground Scintillation Telescope (BUST). Between 1978 December and 2013 December more than 1500 localized gamma-ray bursts occurred in the field of view of the BUST were coincided with the BUST operation periods. No neutrino signal from GRBs was detected. Upper limits on associated gamma-ray burst neutrino production are presented.

Improved methods for detecting gravitational waves associated with short gamma-ray bursts

In the era of second generation ground-based gravitational wave detectors, short gamma-ray bursts (GRBs) will be among the most promising astrophysical events for joint electromagnetic and gravitational wave observation. A targeted search for gravitational wave compact binary merger signals in coincidence with short GRBs was developed and used to analyze data from the first generation LIGO and Virgo instruments. In this paper, we present improvements to this search that enhance our ability to detect gravitational wave counterparts to short GRBs. Specifically, we introduce an improved method for estimating the gravitational wave background to obtain the event significance required to make detections; implement a method of tiling extended sky regions, as required when searching for signals associated to poorly localized GRBs from Fermi Gamma-ray Burst Monitor or the InterPlanetary Network; and incorporate astrophysical knowledge about the beaming of GRB emission to restrict the search parameter space. We describe the implementation of these enhancements and demonstrate how they improve the ability to observe binary merger gravitational wave signals associated with short GRBs.

GRB 080517: a local, low-luminosity gamma-ray burst in a dusty galaxy at z = 0.09

We present an analysis of the photometry and spectroscopy of the host galaxy of Swift-detected GRB 080517. From our optical spectroscopy, we identify a redshift of z = 0.089 +/- 0.003, based on strong emission lines, making this a rare example of a very local, low luminosity, long gamma ray burst. The galaxy is detected in the radio with a flux density of S(4.8GHz) =0.22 +/- 0.04mJy - one of relatively few known GRB hosts with a securely measured radio flux. Both optical emission lines and a strong detection at 22 um suggest that the host galaxy is forming stars rapidly, with an inferred star formation rate ~16 Msun/yr and a high dust obscuration (E(B-V )>1, based on sight-lines to the nebular emission regions). The presence of a companion galaxy within a projected distance of 25 kpc, and almost identical in redshift, suggests that star formation may have been triggered by galaxy-galaxy interaction. However, fitting of the remarkably flat spectral energy distribution from the ultraviolet through to the infrared suggests that an older, 500Myr post-starburst stellar population is present along with the ongoing star formation. We suggest that that the host galaxy of GRB 080517 is a valuable addition to the still very small sample of well-studied local gamma-ray burst hosts.

SHORT VERSUS LONG AND COLLAPSARS VERSUS NON-COLLAPSARS: A QUANTITATIVE CLASSIFICATION OF GAMMA-RAY BURSTS

Gamma-Ray Bursts (GRBs) are traditionally divided to long and short according to their durations (>/< 2 sec). It was generally believed that this reflects a different physical origin: Collapsars (long) and non-Collapsars (short). We have recently shown that the duration distribution of Collapsars is flat, namely independent of the duration, at short durations. Using this model for the distribution of Collapsars we determine the duration distribution of non-Collapsars and estimate the probability that a burst with a given duration (and hardness) is a Collapsar or not. We find that this probability depends strongly on the spectral window of the observing detector. While the commonly used limit of 2 sec is conservative and suitable for BATSE bursts, 40% of swift's bursts shorter than 2 sec are Collapsars and division >/<0.8 sec is more suitable for swift. We find that the duration overlap of the two populations is very large. On the one hand there is a non-negligible fraction of non-Collapsars longer than 10 sec, while on the other hand even bursts shorter than 0.5 sec in the swift sample have a non-negligible probability to be Collapsars. Our results enable the construction of non-Collapsar samples while controlling the Collapsar contamination. They also highlight that no firm conclusions can be drawn based on a single burst and they have numerous implications concerning previous studies of non-Collapsar properties that were based on the current significantly contaminated swift samples of localized short GRBs. Specifically: (i) all known short bursts with z>1 are most likely Collapsars, (ii) the only short burst with a clear jet break is most likely a Collapsar, indicating our lack of knowledge concerning non-Collapsar beaming (iii) the existence of non-Collapsars with durations up to 10 sec impose new challenges to non-Collapsar models.

SELECTION EFFECTS ON THE OBSERVED REDSHIFT DEPENDENCE OF GAMMA-RAY BURST JET OPENING ANGLES

Apparent redshift dependence of the jet opening angles ($\theta_{\rm j}$) of gamma-ray bursts (GRBs) is observed from current GRB sample. We investigate whether this dependence can be explained with instrumental selection effects and observational biases by a bootstrapping method. Assuming that (1) the GRB rate follows the star formation history and the cosmic metallicity history and (2) the intrinsic distributions of the jet-corrected luminosity ($L_{\rm \gamma}$) and $\theta_{\rm j}$ are a Gaussian or a power-law function, we generate a mock {\em Swift}/BAT sample by considering various instrumental selection effects, including the flux threshold and the trigger probability of BAT, the probabilities of a GRB jet pointing to the instrument solid angle and the probability of redshift measurement. Our results well reproduce the observed $\theta_{\rm j}-z$ dependence. We find that in case of $L_{\gamma}\propto \theta_{\rm j}^2$ good consistency between the mock and observed samples can be obtained, indicating that both $L_{\rm \gamma}$ and $\theta_{\rm j}$ are degenerate for a flux-limited sample. The parameter set $(L_{\rm \gamma}, \theta_{\rm j})=(4.9\times 10^{49} \rm {erg\ s}^{-1},\ 0.054 {rad})$ gives the best consistency for the current {\em Swift} GRB sample. Considering the beaming effect, the derived intrinsic local GRB rate accordingly is $2.85\times 10^2$ Gpc$^{-3}$ yr$^{-1}$, inferring that $\sim 0.59%$ of Type Ib/c SNe may be accompanied by a GRB.

Estimating detection rates for the LIGO–Virgo search for gravitational-wave burst counterparts to gamma-ray bursts using inferred local GRB rates

One of the ongoing searches performed using the LIGO–Virgo network of gravitational-wave interferometers is the search for gravitational-wave burst (GWB) counterparts to gamma-ray bursts (GRBs). This type of analysis makes use of GRB time and position information from gamma-ray satellite detectors to trigger the GWB search, and the GWB detection rates possible for such an analysis thus strongly depend on the GRB detection efficiencies of the satellite detectors. Using local GRB rate densities inferred from observations which are found in the science literature, we calculate estimates of the GWB detection rates for different configurations of the LIGO–Virgo network for this type of analysis.

The connection between gamma-ray bursts and supernovae Ib/c

Context. It has been established that Gamma-Ray Bursts (GRBs) are connected to Supernovae (SNe) explosions of type Ib/c. Aims. We intend to test whether the hypothesis of type Ib/c SNe from different massive progenitors can reproduce the local GRB rate as well as the GRB rate as a function of redshift. We aim to predict the GRB rate at very high redshift under different assumptions about galaxy formation and star formation histories in galaxies. Methods. We assume different star formation histories in galaxies of different morphological types: ellipticals, spirals and irregulars, which have already been tested in self-consistent galaxy models reproducing both chemical and photometrical properties of galaxies. We explore different hypotheses concerning the progenitors of type Ib/c SNe: i) single massive stars (M > 25 M� , Wolf-Rayet stars), ii) massive close binaries (12–20 M� ), and iii) both Wolf-Rayet stars and massive binaries. We conclude that the mixed scenario (iii) is preferable to reproduce the local type Ib/c SN rates in galaxies and we adopt this scenario for comparison with the GRB rates. Results. We find an excellent agreement between the observed GRB local rate and the predicted type Ib/c SN rate in irregular galaxies,

Deducing the Lifetime of Short Gamma‐Ray Burst Progenitors from Host Galaxy Demography

The frequency of short gamma-ray bursts (GRBs) in galaxies with distinct star formation histories can be used to constrain the lifetime of the progenitor systems. As an illustration, we consider here the constraints that can be derived from separating the host galaxies into early and late types. On average, early-type galaxies have their stars formed earlier than late-type galaxies, and this difference, together with the time delay between progenitor formation and short GRB outburst, leads to different burst rates in the two types of hosts. Presently available data suggest, but do not yet prove, that the local short GRB rate in early-type galaxies may be comparable to that in late-type galaxies. This suggests that, unlike Type Ia supernovae, at least half of the short GRB progenitors that can outburst within a Hubble time have lifetimes greater than about 7 Gyr. Models of the probability distribution of time delays, here parameterized as P(τ) ∝ τn, with n ≳ -1 are favored. This apparent long time delay and the fact that early-type galaxies in clusters make a substantial contribution to the local stellar mass inventory can explain the observed preponderance of short GRBs in galaxy clusters.

Short gamma-raybursts as a possible probe of binary neutron star mergers

We study the properties of short gamma-ray bursts (GRBs), basedon the assumption that they are all connected to binaryneutron star mergers, whose mechanism contains a largeamount of uncertainty. In particular, the merger timedistribution, which is essential for short GRBrate estimation, is focused on; we parametrize it simply as Pm(t)∝tα with a lower cut-off timescale τ. The short GRBrate, calculated using such a parametrization with a specificmodel of the cosmic star formation rate, is found to be quiteinsensitive to the value of τ, but very sensitiveto α. With such formation rate models, the peak fluxdistribution observed by BATSE is fitted. In the fittingprocess, the local short GRB rate ρ0 is treated as one ofthe free parameters, giving the best fit when ρ0 = 0.1–2 yr−1 Gpc−3, depending on the other freeparameters as well as the formation rate model represented by(τ,α). We also discuss several implications for theintrinsic properties of possible sources of short GRBs, such asjet structure, intrinsic luminosity function, and intrinsicduration distribution.

Self-compression and catastrophic collapse of photon bullets in vacuum

Photon-photon scattering, due to photons interacting with virtual electron-positron pairs, is an intriguing deviation from classical electromagnetism predicted by quantum electrodynamics (QED). Apart from being of fundamental interest in itself, collisions between photons are believed to be of importance in the vicinity of magnetars, in the present generation intense lasers, and in intense laser-plasma/matter interactions, the latter recreating astrophysical conditions in the laboratory. We show that an intense photon pulse propagating through a radiation gas can self-focus and, under certain circumstances, collapse. This is due to the response of the radiation background, creating a potential well in which the pulse gets trapped, giving rise to photonic solitary structures. When the radiation gas intensity has reached its peak values, the gas releases part of its energy into “photon wedges,” similar to Cherenkov radiation. The results should be of importance for the present generation of intense lasers and for the understanding of localized gamma-ray bursts in astrophysical environments. They could furthermore test the predictions of QED and give means to create ultraintense photonic pulses.

Radio Imaging of Gamma-Ray Burst Jets in Nearby Supernovae

We calculate the time evolution of the flux, apparent size, and image centroid motion of gamma-ray burst (GRB) radio jets and show that they can be resolved by the Very Long Baseline Array (VLBA) at distances of hundreds of megaparsecs. We find that GRB 030329, which showed spectroscopic evidence for an associated Type Ic supernova (SN) at a distance of ≈800 Mpc, might just be resolvable by VLBA after several months. The prospects are much better for jets that are oriented sideways in similar SNe with no GRB counterpart; in particular, the motion of the flux centroid in such jets can be detected by the VLBA up to , even when the z ∼ 1 jet cannot be resolved. If most GRBs are accompanied by a Type Ib/c SN, then there should be a few SN/GRB jets per year within a distance 200 Mpc, and most of them would be oriented sideways with no gamma-ray or X-ray precursor. Detection of these jets can be used to calibrate the fraction of all core-collapse SNe that produce relativistic outflows and determine the local GRB rate. Overall, the rate of Type Ib/c SNe that do not produce a GRB at all, but rather make relativistic radio jets with an initial Lorentz factor of a few, may be larger by up to 2 orders of magnitude than the rate of those that produce GRBs. Subject headings: gamma rays: bursts — ISM: jets and outflows — supernovae: general On-line material: color figures